In typical banknote handling apparatuses used in financial institutions and the like, banknotes taken in the apparatus are subjected to denomination recognition or authenticity recognition by a banknote recognition apparatus incorporated in the banknote handling apparatus. The banknote recognition apparatus includes a line sensor that acquires an image of a banknote that is being transported on a transport path, a thickness detecting sensor that detects a thickness of the banknote, and a magnetic sensor that detects magnetic characteristics of the banknote. The banknote recognition apparatus acquires characteristics of the banknote by using these sensors and performs the various recognition processes on the banknote.
For example, Japanese Patent Application Laid-open No. 2006-227951 discloses an apparatus in which a paper sheet is pinched between a transport roller arranged on a transport path and an opposite roller arranged opposing the transport roller, the paper sheet is transported by the transport roller driven by a motor, and various recognition processes are performed on the paper sheet while transporting the paper sheet. Moreover, International Patent publication WO2011/096258 discloses an apparatus in which a magnetic pattern formed on a medium is detected while the medium is being transported by a transport device that includes rollers and guides.
In the conventional apparatuses, however, magnetization is induced in the transport roller, which is made of metal, by a magnet used in the magnetic sensor for detecting magnetism.
Most magnetic sensors use a magnet for detecting magnetism. Concretely, a bias magnetic field is generated around a magnetic sensor by arranging a magnet near the magnetic sensor. Magnetic material, such as a magnetic ink or a magnetic thread, incorporated in a paper sheet is detected based on a magnetic flux change as the magnetic material passes through the bias magnetic field. In such a configuration, for example, the magnet used to magnetize the magnetic material is arranged upstream of the magnetic sensor on the transport path. Although the transport path is supposed to transport only the paper sheets, magnetic metal members, such as paper clips or stapler needles used to bundle banknotes, may be accidentally transported on the transport path. Such magnetic metal members get magnetized when they pass near the magnet arranged along the transport path. If the magnetized metal members may touch the transport roller, the transport roller gets magnetized. A variation of the bias magnetic field around the magnetic sensor is caused by rotation of such a magnetized transport roller. This variation acts as a noise and the detection accuracy of the magnetism by the magnetic sensor is degraded. In order to cope with the recent demand for downsizing the apparatus, the magnet and the transport roller or the transport roller and the magnetic sensor are arranged close to each other. Accordingly, there is a possibility that the transport roller is disadvantageously magnetized when even a small magnetic metal member is transported on the transport path. Moreover, during the maintenance work, if a magnetic screwdriver touches the transport roller by mistake, the transport roller is disadvantageously magnetized.
One approach to address and solve this issue is to use a roller made entirely of a non-magnetic metal; however, the durability of such a roller is disadvantageously low. On the other hand, if a ceramic bearing, which is non-magnetic and has high durability, is used for the transport roller, the cost disadvantageously increases. If a bearing is used for the roller in the transport path, it is desirable to use a metal bearing instead of a ceramic bearing from the viewpoint of cost. Also, it is desirable to use a magnetic metal bearing instead of a non-magnetic metal bearing from the viewpoint of durability. Thus, there is a requirement for a technology that can solve the problem of magnetization of the roller even when a bearing and the like made of magnetic metal that is less expensive but has a high durability is used for the roller.